Effect of curing regimes on mechanical properties and microstructure of engineered cementitious composites with full desert sand

Abstract

To establish a curing regime that facilitates the rapid enhancement and stable progression of early-age strength and tensile ductility in engineered cementitious composites with full desert sand (DSECC), aligning with production efficiency, this study examines the effects of different curing regimes (standard curing, natural curing, 20℃ water curing, and 90℃ water bath curing) on DSECC 's the mechanical properties and microstructure. The findings indicate that 90℃ water bath curing is beneficial to enhance the mechanical properties of DSECC, and its early 7 days strength and tensile deformation capacity (up to 7.05 %) can reach or exceed the standard curing 28 days level. In the uniaxial tensile test, samples cured in 20℃ water exhibit increased crack widths and reduced crack numbers, resulting in a sharp decline in the ultimate tensile strain from 4.96 % at 14 days to 1.57 % at 28 days. Natural curing leads to regression in strength at 28 days. The microstructure analysis revealed that 90℃ water bath curing fostered the development of high-density C-S-H gel and the dissolution of desert sand, while preserving the integrity of the fibers, enhancing the fiber-matrix interface transition zone (ITZ). The pore characteristic parameters under 90℃ water bath curing are superior, which has a notable refinement of the DSECC matrix's pore size. 20℃ Water curing can make up for the defects caused by desert sand and improve the compactness of matrix-aggregate ITZ. Natural curing yields the lowest degree of matrix hydration, with porosity reaching as high as 41.90 %, and pores smaller than 50 nm accounting for only 8.97 %.